1. Field of the Invention
The present invention relates to an EL (electroluminescent) device sealing plate, a multiple sealing plate-producing mother glass substrate for producing a plurality of the EL device sealing plates, and an EL device, and in particular to a flangeless EL device sealing plate that has peripheral projecting parts and covers an EL multilayer film formed on an EL device substrate, a multiple sealing plate-producing mother glass substrate for producing a plurality of the EL device sealing plates, and an EL device.
2. Description of the Related Art
An EL device is generally constituted from a transparent substrate, an EL multilayer film formed on the substrate, and an EL device sealing plate that is joined to the substrate by a joining material or the like so as to hermetically cover the EL multilayer film.
In an EL device of first prior art as proposed, for example, in Japanese Laid-open Patent Publication (Kokai) No. 2000-156287, Japanese Laid-open Patent Publication (Kokai) No. 2000-195662, Japanese Laid-open Patent Publication (Kokai) No. 2000-260562, Japanese Laid-open Patent Publication (Kokai) No. 2001-167875, and Japanese Laid-open Patent Publication (Kokai) No. 2001-176655, an adsorbing agent that adsorbs moisture and oxygen is disposed in a space in which an EL multilayer film is sealed to adsorb moisture and oxygen that constantly infiltrates into this space from the outside.
Moreover, in an EL device of second prior art as proposed in Japanese Laid-open Patent Publication (Kokai) No. 11-40354, a protective film is provided on the EL multilayer film itself.
Furthermore, in an EL device of third prior art as proposed in Japanese Laid-open Patent Publication (Kokai) No. 10-172757, an EL multilayer film is sealed in by disposing a low-melting-point metal around the outer periphery of parts to be joined and then melting the low-melting-point metal; in an EL device of fourth prior art as proposed in Japanese Laid-open Patent Publication (Kokai) No. 2001-92376, an EL multilayer film is sealed in by disposing a metal such as Cr around the outer periphery of parts to be joined, and then momentarily heating the metal using laser light to melt and thus join the parts to be joined. Moreover, there have also been proposed EL devices in which spacers or the like are interposed between parts to be joined, and then joining is carried out including the spacers, thus sealing in an EL multilayer film.
As described above, the first to fourth prior art is all art for resolving the problem of an EL multilayer film deteriorating due to moisture and oxygen that infiltrates in from the outside of an EL device.
On the other hand, an EL device sealing plate may be made of a metal, a glass, a resin, and so on. In the case of a glass EL device sealing plate, methods of processing a starting material glass plate into a recessed shape to produce the glass EL device sealing plate include a pressing method in which the starting material glass plate itself is bent, and a sandblasting method and an etching method in which a central part of the starting material glass plate is removed. In the sandblasting method or the etching method, peripheral parts of the starting material glass plate are masked, and then the central part is sandblasted or etched to form a recessed part in the central part.
However, with the first to fourth prior art described above, although infiltration of moisture and oxygen into the EL device can be prevented, no consideration is given to the area of the parts of the sealing plate to be joined to the substrate in the EL device, and this area may be insufficient.
Moreover, with the pressing method described above, parts of the sealing plate that contact the substrate of the EL device in which the sealing plate is used, i.e. parts that are joined to the substrate, are flange-shaped, and hence the area thereof can be made sufficiently high, but these parts have a low degree of flatness, and hence when these parts are joined to the substrate using an adhesive when manufacturing the EL device, the thickness of the adhesive is not uniform, and thus moisture and oxygen are liable to infiltrate into the EL device via these joining parts.
Furthermore, with the sandblasting method described above, a large number of minute cracks that are inherent in the sandblasting method arise in the sealing plate, and hence the strength of the sealing plate drops. In particular, in the case that the EL device in which the sealing plate is used is a top emission type EL device for use in a mobile telephone or the like, the sealing plate will be subjected to external pressure, and hence the sealing plate will be required to have sufficient strength to such external pressure.